Semi-aliphatic polycarbonates toughening agents with cyanate ester resins yield polycyanurate compositions

Material offers significant improvements in mechanical toughness while maintaining strength, heat resistance, moisture resistance, and other desirable properties


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Polycyanurates are plastics with high thermal stability which are used in structural composites for the aerospace applications. Relative to epoxy resins they have better thermal and dielectric properties as well as lower moisture absorption.

Navy scientists have been able to push the performance properties of polycyanurates with the development of a semi aliphatic polycarbonate as a starting material. This includes an amorphous polycarbonate being a structure of a random copolymer of polybisphenol A carbonate and 4,4′-(3,3,5-trimethylcyclohexylidene) diphenol carbonate. The two co-monomers enable a balance between mechanical strength and thermal stability (provided by the aromatic segment) on the one hand, and moisture resistance and deformability on the other.

Selection of monomers and molecular weight (typically 2,000-100,000 g/mol), allows the material scientist to obtain a polycarbonate composition that best balances these properties depending on the desired application. The polycarbonates are utilized in the form of powder or pellets and ground readily into a fine suspension that is easily dispersed.

In order to formulate the resin system, the finely dispersed polycarbonate is liquefied either by dissolution in a solvent with a high vapor pressure, including methylene chloride, or by suspending directly into a reactive monomer. Once liquefied, the polycarbonate is added to a mixture of reactive cyanate ester monomers.

Upon heating to moderate temperatures, from 25° C. to 200° C. depending on the application, the liquid becomes of a viscosity such that it is easily poured into a mold and out of which any dissolved air may escape in less time (hours) than needed to complete the curing reaction. Molds may be any type of polymeric, ceramic, or metal insert, sheet, flake, powder, or fibrous matter, into which the liquid penetrates to form a structure generally free of voids.

Applications of APC-toughened cyanate ester resin include missile and aircraft airframes (parts that require continuous service temperatures of around 200 to 400° F.), radomes, firewalls, ship topside structures, solar concentrators, coatings for heat and fire resistance, insulation, including electrical conduits, printed circuit boards and chip housings, remotely operated sensor array housings, emergency response vehicles including fire trucks, blast shields, engine or fuel cell housings, and emergency water dispensers/safety showers.

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